1. Field of the Invention
The present invention relates to an optical fiber coil which can be used in a fiber-optic gyroscope, sensor, optical amplifier, laser, dispersion compensator, nonlinear optical device, delay circuit, dummy circuit, other parts employing long optical fibers, extra long handling tool, etc., and which can be used to conserve space and have low tension, and the present invention also relates to a production method for the optical fiber coil.
2. Description of Related Art
Optical fiber type devices that employ optical fibers therein are widely employed in, for example, sensors. In addition, such optical fiber type devices have attracted attention for use in optical fiber amplifiers that are doped with erbium, thulium, praseodymium, etc., dispersion compensators using dispersion-compensated optical fibers, and nonlinear optical devices.
It is known that optical fiber type devices are superior devices, that connectivity thereof with transmission paths or to other devices is superior, that they are less likely to be affected by external noise, and that they have stable characteristics, because they are constituted of optical fiber.
However, they are disadvantageous in that the optical fiber is bulky when the desired length thereof is long. In order to avoid this problem, an optical fiber coil which is wound around a small bobbin, etc., can be used.
As a general production method for the optical fiber coil, initially, in a first process, an adhesive is applied to a part or the entirety of the surface of one long single optical fiber to form an adhesive layer. The adhesive layer is provided on at least part of the surface of the single optical fiber, so that proximate optical fibers are adhered and fixed to each other when the single optical fiber is wound in a coiled state.
In a subsequent process, the single optical fiber provided with the adhesive layer is wound in a coiled state around a bobbin having a desired diameter by using a coil winding device. At this time, in order to make the coil as compact as possible by minimizing spaces between the single optical fibers, the single optical fiber is wound under conditions in which stress is applied thereto.
The adhesive layer is then dried or cured using a suitable method, and an optical fiber coil having the desired winding diameter, winding width, and winding length, can be produced (see Japanese Unexamined Patent Application Publication No. 2003-107250).
FIG. 8 shows a sectional view of a conventional optical fiber coil. Reference numeral 1 indicates single optical fibers, reference numeral 5 indicates a bobbin, reference numeral 100 indicates a conventional optical fiber coil, and reference letter H indicates a central hole.
As shown in FIG. 8, the conventional optical fiber coil 100 is formed by simply winding the single optical fiber 1 on the bobbin 5.
However, there are problems in the above conventional production method for an optical fiber coil.
That is, since the single optical fibers are exposed to the surface of the fiber coil, optical transmission loss easily occurs due to slight stress or temperature change. As a result, in the case in which the single optical fiber is accurately wound in a coiled state in order to avoid the above loss, it is expensive because of the need for adjustment thereof, or the like.
In addition, when the winding density of the coil is too high, stress is applied to the single optical fibers and optical transmission loss occurs.